To understand, first you need to know just what tickling is. Tickling refers to 2 different types of sensations. The first is knismesis, which is when something just barely touches your skin and makes you want to scratch the area, like when a bug crawls on your skin. But gargalesis is the type of tickling that causes you to laugh, and it’s characterized by harder contact that releases the confusing reactions of pain and pleasure.

All mammals experience knismesis. But gargalesis is only experienced by rats and primates, which includes humans, and all primates are mostly ticklish in the same spots, such as under the ribs, arms, and chin. Since these are all vulnerable areas, some researchers think gargalesis is an evolutionary mechanism that is used to teach self defense.

When tickled, people kick and twist, but they also smile and laugh. The positive facial expressions communicate that the person being tickled wants more. So the thinking goes that if tickling produced negative facial expressions, then we wouldn’t tickle each other, and we wouldn’t learn how to defend ourselves

Who knew?

Another strange thing that science has discovered about tickling is where it comes from in the body. Apparently, it is generated from our pain nerves. After operations where surgeons have severed pain nerves from skin, the ability to be tickled is heavily diminished. This fuels the evolutionary theory of self defense. After all, the pain nerves would logically be the natural home for the ticklish feeling if it was all about defending yourself.

Even though evolutionary science has provided this answer, it’s interesting to note that the father of evolution, Charles Darwin, had some really weird ideas about what caused tickling. Darwin thought that tickling was produced from people being in a light state of mind when being tickled. This theory seems to be easily disprovable, as there are many accounts of people being tickled successfully, even when in a negative mindset. However, Darwin continued to argue that the ticklish feeling was produced through a state of mind, noting that people anticipate the pleasure of tickling, even when they are depressed.

Psychologists also think that tickling is an important part of childhood development. While many parents will tickle their children for fun, the psychologists say that they may not realize that they’re also instinctively teaching their children to trust their touch and to differentiate this touching from less innocent forms of touching.

If you hate being tickled, you’re not alone. In fact, in a survey, researchers discovered that the most common answer to the question, “do you like being tickled?” was no. In this survey, 36% of people stated that they didn’t like being tickled, while 32% said that they did, and the remaining 32% said that they were indifferent.

Also, you may be wondering what percentage of people are ticklish, and in which areas. Luckily, researchers have provided stats on this too. A 2008 study revealed that 73% of people are ticklish. The area of the body that is ticklish in most people might surprize you. It’s actually the right foot. 89% of ticklish people feel the sensation here. The left foot also reported high levels of ticklishness, with 77% of respondents feeling the sensation. Other highly ticklish areas are under the arms (80% of people,) on the ribs (77%,) the palms of the hands (65%,) and the knee caps (61%.) Also, this research discovered that there is no difference in ticklishness between the genders. Men and women are equally ticklish, it seems.

Another weird fact of tickling is this: some schizophrenics can tickle themselves. This appears to be due to the fact that often people with the condition do not recognize that they are the people doing the tickling. This likely has implications in how scientists can further understand tickling, and clearly more research needs to be done.

Tickling as a legal punishment has been practised throughout history, across a range of cultures. In China during the Han Dynasty, tickle torture was a punishment that courts would give to noblemen and women who had broken the law. It was used because it left no marks and would not mean a long recovery for the important person. Additionally, in ancient Rome, a punishment existed that involved dipping someone’s feet in a saltwater solution and getting a goat to lick the solution off, causing a tickling feeling. However, as a goat’s tongue is very course, the sensation became more painful as it progressed.